Fix invalidating attachment's blob in test

Using `load_defaults` for Rails 6.1 (see 31712c2) makes
`active_storage.track_variants` true by default.

Here we remove the overridden setting and adapt our test to invalidate
the blob with the new default in place.

See also rails/rails#37901

backend/spec/features/admin/products/edit/images_spec.rb

@@ -78,7 +78,7 @@
         end
 
         click_button "Update"
-        Spree::Image.first.attachment.blob.update(key: 11)
+        invalidate_attachment(Spree::Image.first.attachment)
         visit current_path
         expect(page).to have_xpath("//img[contains(@src, 'assets/noimage/mini')]")
       end
@@ -136,4 +136,12 @@
       expect(page).to have_css("thead th", count: 4)
     end
   end
+
+  def invalidate_attachment(attachment)
+    blob = attachment.blob
+    blob.variant_records.each do |variant_record|
+      variant_record.update(variation_digest: SecureRandom.uuid)
+    end
+    blob.update(key: SecureRandom.uuid)
+  end
 end

core/lib/spree/testing_support/dummy_app.rb

@@ -47,10 +47,8 @@ def self.setup(gem_root:, lib_name:, auto_migrate: true)
 
   class Application < ::Rails::Application
     config.load_defaults("#{Rails::VERSION::MAJOR}.#{Rails::VERSION::MINOR}")
-    # TODO: Remove the two following settings once the codebase has been adapted
-    # to load_defaults
+    # TODO: Remove once the codebase has been adapted to the new default
     config.active_record.has_many_inversing = nil
-    config.active_storage.track_variants = nil
     config.eager_load = false
     config.cache_classes = true
     config.cache_store = :memory_store